Remotely powered electronic devices and related systems are known. For example, U.S. Pat. No. 5,009,227 issued to Geiszler et al. entitled Proximity Detecting Apparatus, discloses a remotely powered device which uses electromagnetic coupling to derive power from a remote source and then uses both electromagnetic and electrostatic coupling to transmit stored data to a receiver often collocated with the remote source. Such remotely powered communication devices are commonly known as radio frequency identification ("RFID") tags.
Earlier RFID tags and systems primarily use electromagnetic coupling to remotely power the remote device and couple the remote device with an exciter system and a receiver system. The exciter system generates an electromagnetic excitation signal used to power up the device and cause the device to transmit a signal including stored information. The receiver receives the signal produced by the remote device.
Known electromagnetic coupling mechanisms include an oscillator as part of the exciter system and a coil antenna on both the exciter system and the remote tag that employs the identification device, including an electronic circuit. For example, in an earlier system, excitation circuitry is connected to a coil antenna that radiates excitation signals that are picked up by a coil antenna mounted on a tag that contains the electronic circuit. The excitation signals energize the circuit, which then provides an information-carrying signal that is transmitted to the receiver using electromagnetic or electrostatic coupling.
One problem with the use of electromagnetic coupling between a remote device and either an exciter or a receiver has been the complexity involved in the manufacture of remote devices that employ a coil antenna. The spiral layout of a typical coil antenna makes it more difficult to produce, increases cost and also the size of the remote device. The coil antennas require tight tolerances for efficient performance. Additionally, typical coil antennas have undesirable thermal compression characteristics that affect, in particular, the ability to create a flat tag or remote device that encompasses the coil.
Radio frequency identification tags and associated systems have numerous uses. For example, radio frequency identification tags are frequently used for personal identification in automated gate sentry applications protecting secured buildings or areas. These tags often take the form of access control cards. Information stored on the radio frequency identification tag identifies the person seeking access to the secured building or area. Older automated gate sentry applications require the person accessing the building to insert or swipe their identification tag into or through a reader for the system to read the information from the identification tag. Newer radio frequency identification tag systems allow the radio frequency identification tag to be read at a short distance using radio frequency data transmission technology, thereby eliminating the need to insert or swipe an identification tag into or through a reader. Most typically, the user simply holds or places the radio frequency identification tag near a base station, which is coupled to a security system securing the building or area. The base station transmits an excitation signal to the radio frequency identification tag that powers circuitry contained on the radio frequency identification tag. The circuitry, in response to the excitation signal, communicates stored information from the radio frequency tag to the base station, which receives and decodes the information. The information read is used by the security system to determine if access is appropriate. Also, radio frequency identification tags may be written remotely by an excitation signal appropriately modulated in a predetermined manner.
In addition to typical applications for access control of persons, RFID tags may be useftil in electronic animal identification, baggage tracking, parcel tracking, inventory management applications, asset identification and tracking, and other applications involving identification of things. These applications involve transmitting stored information from a tag to an exciter/reader system in close proximity with the tag. Also, these applications may involve writing information to a tag. RFID tags for these applications may need to be durable for long-term use or disposable, for temporary use.
In applications for identification of persons and things, bar codes are almost universally employed. Generation of the bar code is very inexpensive. However, one problem associated with bar codes and bar code readers is that the bar codes must be precisely aligned with the bar code reader in order to be read. Another problem with bar codes is that the bar codes may become unreadable as a result of damage, for example, exposure to moisture, or wear and tear from use. RFID tags address some of the shortcomings of bar codes.
In addition to the need to transmit stored information via radio frequency transmission, it is often desirable for an RFID tag to have indicia perceptible to persons, including printed information, logos, photographs or other printed or graphical data. In many applications, the printed indicia must be customizable for a single use, necessitating the ability to print or otherwise place indicia directly on the RFID tag. This requires the RFID tag to be very thin, very flat and flexible to be compatible with existing printing technologies, including dye sublimation printing, ink jet printing and flexographic printing. Prior RFID tags incorporating coils are limited in their ability to be flat, thin and flexible, not to mention the associated cost. This has limited their ability to be printed, particularly in the area near the coil antenna.
Therefore, there is a need for a thin, flat, flexible, printable radio frequency identification tag.